1. Field of the Invention
This invention relates to a plastisol-lined metal closure of the type which may be applied to a helically threaded finish of a glass or rigid plastic container by a press-on action, but which may be normally removed from the finish of the container only by a twisting action. More particularly, this invention relates to a press-on, twist-off plastisol-lined metal closure with improved top load resistance.
2. Description of the Prior Art
U.S. Pat. No. 4,552,279 (Mueller, et al.), which is assigned to the assignee of this application, describes a press-on, twist-off closure which is made up of a cup-shaped metal closure with a foamed vinyl plastisol material which is cast in situ within the closure to cover a portion of the inside of a base wall of the closure and a surrounding peripheral wall, to thereby engage the top rim and a portion of the side of the finish of a container upon the application of the closure to the container. After operations to shape and cure the plastisol lining of the closure, the closure is pressed upon the externally threaded finish of the container, the threads of the container forming threads in the plastisol lining after the application of the closure to the container to preclude normal removal of the closure from the container other than by a twisting action. Containers capped with closures of this type have heretofore been packaged in closed top corrugated fibreboard trays, each of the trays being closed by the infolding of top flaps at the tops of the side walls of the trays, as is known in the art. Even though such trays are usually superimposed several deep during shipment and storage, such closures, which are normally flush with the top of the tray and which, therefore, bear a part of the weight of the filled tray or trays thereabove, provide satisfactory top load resistance to those superimposed filled trays, but to a substantial extent as a result of the cushioning effect of the top structure of the closed top of the tray, which serves to fairly evenly distribute the superimposed loads from container to container within the tray and around the circumference of the closure on each container in the tray.
One of the recent advances in the packaging field is the use of open top trays in the packaging of containers closed with press-on, twist-off closures, since trays of this type use appreciably less corrugated fibreboard than their closed top counterparts and are, hence, appreciably less expensive. However, the use of open top trays can result in greater and less evenly distributed top loads on the closures of the containers packaged in any such tray which may be at or near the bottom of a stack of such trays, and this can result in a failure of the seal between any such closure and the container to which it is affixed. This problem can be particularly annoying when closures are used in the packaging of a liquid, for example, an infant juice formulation, which is a packaging application that frequently uses plastisol-lined closures.
U.S. Pat. No. 4,576,299 (Lecinski, Jr.) describes a press-on, twist-off plastisol-lined metal closure which claims to have improved top load leakage resistance. However, it is believed that closures according to this reference do not have adequate top load leakage resistance for use in many applications where the containers capped with such closures are packed in open top corrugated trays. Other types of press-on, twist-off lined metal closures are illustrated in U.S. Pat. Nos. 3,270,904 (C. N. Foster, et al.) 3,371,813 (R. C. Owen, et al.), 3,448,881 (D. H. Zipper), 3,685,677 (Westfall), 3,690,497 (Lecinski, Jr.), 3,741,423 (Acton, et al.), 4,000,825 (Westfall), and 4,603,786 (Lecinski, Jr.), but it is believed that closures of each of these references lack adequate top load leakage resistance for use on containers packaged in open top trays.